In a turn of events, Republicans – despite multiple attempts over the last decade to repeal and replace President Barack Obama’s signature healthcare legislation – are now coming to the beleaguered law's defense.

Interested in Donald Trump?

Add Donald Trump as an interest to stay up to date on the latest Donald Trump news, video, and analysis from ABC News.

They are motivated by concerns over whether the Trump administration’s argument to gut popular provisions of the Affordable Care Act could win in a federal court. If those efforts are successful, tens of millions of people could stand to lose access to affordable health insurance that includes coverage for pre-existing conditions.

“There’s no way Congress is going to repeal protections for people with pre-existing conditions who want to buy health insurance,” said Tennessee Sen. Lamar Alexander, chairman of the Senate’s Health, Education, Labor and Pensions committee.

The Republican senator blasted Attorney General Jeff Sessions for refusing to defend the constitutionality of protections for Americans with pre-existing conditions in a federal lawsuit, calling Sessions’ argument as “far-fetched as any” he’s ever heard.

The Texas-led lawsuit filed earlier this year claims that Congress’ decision to eliminate the individual mandate penalty, which goes into effect in 2019, should render the entire health care law invalid.

Evan Vucci/AP

Attorney General Jeff Sessions listens during the White House Opioid Summit in the East Room of the White House, March 1, 2018, in Washington, D.C.

In a court filing last week, the Trump administration urged the Texas federal court to strike down two specific provisions from the ACA: one that requires insurers to cover people with pre-existing conditions, and the other that prevents insurers from charging individuals a higher premium because of their pre-existing condition.

But the administration said the rest of the law, including Medicaid expansion, can remain in place.

“I didn’t hear a single senator say that they also thought they were repealing protections for people with pre-existing conditions,” Alexander said in a terse statement.

A 2016 Kaiser Foundation analysis found that 52 million adults under the age of 65 have pre-existing conditions that would likely make them uninsurable if they weren’t protected under insurance regulation changes made by the ACA.

“I support coverage of pre-existing conditions. I don't know about the lawsuit, I haven't read the briefs and the pleadings, I can just tell you I support coverage of pre-existing conditions,” GOP Sen. John Kennedy of Louisiana told ABC News.

At least one Republican senator is now floating the idea of passing legislating to protect coverage for pre-existing conditions as an answer to the lawsuit.

“If a court were to rule that what remains of Obamacare is invalid, I would work to pass new legislation ensuring people with pre-existing conditions have access to good health insurance,” GOP Sen. Bill Cassidy of Louisiana said in a tweet. “As a doctor, I've always put patients first, and this would be no exception.”

According to healthcare.gov, a pre-existing condition is a health problem a person has before enrolling in a new health care plan.

Epilepsy, cancer, diabetes, lupus, sleep apnea, and pregnancy are all examples of pre-existing conditions. Mental disorders, including depression and anxiety, are also considered pre-existing conditions.

Health and Human Services Secretary Alex Azar attempted to distance himself from the administration at a hearing on Tuesday, and said the Justice Department’s stance is a “constitutional and legal position, not a policy position.”

“This, Mr. Secretary, is like some kind of sick joke,” Sen. Maggie Hassan, D-NH, said during the hearing.

Senate Majority Leader Mitch McConnell came to the defense of the healthcare law on Tuesday.

“Everybody I know in the Senate — everybody — is in favor of maintaining coverage for pre-existing conditions,” Senate Majority Leader Mitch McConnell told reporters Tuesday in the Capitol. “There is no difference in opinion about that whatsoever.”

But the alarm rippling across both sides of the aisle is also turning into a political blame game.

McConnell pointed a finger at Democrats for refusing to back previous legislative efforts to stabilize the health care market.

Earlier in the year, GOP Sens. Alexander, Susan Collins of Maine and Democratic Sen. Patty Murray of Washington crafted a bill that would attempt to lower premiums for individuals who buy their coverage in exchange for some flexibility for some states.

“The president had agreed to sign it. And then the Democrats backed away, I think hoping there would be some kind of health care crisis in the fall,” McConnell said. “But make no mistake about it, whatever mess occurs could have been avoided by the bipartisan [agreement].”

Democrats, for their part, are calling out Republicans for what they see as a flip in policy.

“If every Republican now supports protecting pre-existing conditions, that’s news to very sick patients across the country…,” Sen. Patty Murray of Washington said in a statement.

Democrats have vowed to make health care a major issue this summer ahead of the midterm elections.

The Trump administration’s move plays right into the hands of Democrats, who have said they plan to force votes on the issue, likely in a move to alienate Republicans from their voters.

“If Republicans are serious about maintaining protections for people with pre-existing conditions, they should join us in urging the Trump administration to reverse their shameful decision to not defend the constitutionality of that vital provision that is already the law,” Sen. Chuck Schumer said in a statement.

House Democrats fired off a letter to the Department of Justice on Thursday demanding internal documents on Sessions’ decision not to defend the healthcare law.

"First, you appear to have abandoned a longstanding, bipartisan commitment by the Department of Justice to defend duly enacted federal statutes in federal court," the democrats wrote in a letter to Sessions. They also requested a briefing from the Justice Department to explain their decision.

In a separate letter sent to the Department of Health and Human Services, House Democrats are demanding answers on HHS' involvement in DOJ's decision, and if HHS or Centers for Medicare and Medicaid Services conducted any analysis on the impact the lawsuit could have on the health care system prior to DOJ’s announcement, and if they have developed any contingency plans for the "chaos and confusion that would result if DOJ prevails."

One Republican senator so far has signaled he’s supportive of the lawsuit: the junior senator from the state of Texas, home to the federal court now charged with deliberating the merits of the ACA.

“If the court ultimately agrees with the state of Texas and agrees with what the Department of Justice acknowledged the law was, the result will be more choices for health care consumers, more competition more option, more freedom, and lower premiums,” Sen. Ted Cruz told ABC News.